The present invention relates to a plasma process detecting sensor which monitors a physical phenomenon of a plasma state developed by plasma etching of a dry etching process corresponding to part of a semiconductor manufacturing process, and a manufacturing method of the plasma process detecting sensor, and further relates to a method for manufacturing a semiconductor device, using the plasma process detecting sensor.
As techniques each related to a plasma monitoring system using a plasma process detecting sensor for monitoring the process of treating a wafer disposed within a plasma processing apparatus, there have heretofore been known ones described in patent documents 1 and 2 (Japanese Unexamined Patent Publication No. 2003-282546 and Japanese Unexamined Patent Publication No. 2005-236199).
The conventional plasma process monitoring system described in each of the patent documents 1 and 2 is provided with a plasma processing apparatus. The plasma processing apparatus is of an apparatus that generates a plasma within a plasma chamber set to a vacuum state by application of a high-frequency (hereinafter called “RF”) bias and performing etching and deposition or growth on a wafer corresponding to an object to be monitored placed on a stage. A plasma process detecting sensor is attached or affixed onto the wafer.
When the monitoring of a plasma process is performed, a plasma occurs in the plasma chamber by application of the RF bias and a plasma process (e.g., plasma etching process) is performed on the wafer. Upon the plasma etching process, etching occurs by launching positive ions (positive holes) h and electrons e generated by the plasma into a film to be etched. At this time, the time of completion of the plasma etching can be detected by observing a voltage value detected by the plasma process detecting sensor, whereby high-precision machining of the wafer is enabled.
The plasma monitoring system using the conventional plasma process detecting sensor however involves the following problems or imperfections.
Upon processing for forming a large-scale integration (hereinafter called “LSI”) on a wafer, for example, a plurality of contact holes are formed by plasma etching. Since, however, both a potential at the surface of the wafer and a potential at the bottom of each contact hole cannot be monitored in the prior art, charge polarization (charge-up) due to the storage of an electric charge cannot be measured. When an aspect ratio (ratio of a depth of contact hole to the diameter thereof) is high, electrons e are hard to reach the bottom of the contact hole (electron blocking effect). Therefore, the bottom of each contact hole falls short of the supply of the electrons e. As compared with the surface of a contact hole pattern, the contact hole bottom is charged up to plus. These cause problems such as an electrical breakdown of a transistor, a reduction in etching rate, non-progression of etching, etc. Since a contact hole diameter in a leading-edge 65 nm generation or latter is φ0.1 μm and an aspect ratio is as large as 10, the charge-up becomes a serious problem.
In order to solve such imperfections, the inventors, et al. of the present application have previously made such a proposal as shown in FIG. 5 (this previous proposal is not publicly known).
FIG. 5 is a schematic sectional view showing a plasma process detecting sensor previously proposed by the inventors, et al. of the present application.
The plasma process detecting sensor 10 measures the states of electrons e and positive ions h generated by a plasma 21 and has a substrate (e.g., silicon substrate) 11. An insulating film 12 such as a silicon oxide film is formed on the silicon substrate 11. A first electrode (e.g., a lower electrode) 13 comprised of a conductive material such as polysilicon is selectively formed on the insulating film 12. An insulating film 15 comprised of a silicon oxide film or the like is deposited on the first electrode 13. A second electrode (e.g., an upper electrode) 15 comprised of a conductive material such as polysilicon is selectively formed on the insulating film 14.
A contact hole pattern comprised of a plurality of contact holes 16 circular in cross section, which are formed in a wafer actually are formed in the upper electrode 15 by dry etching (e.g., plasma etching). In each of the contact holes 16, for example, a hole diameter (bore diameter) D1 circular in section is about 100 nm, and a hole depth D2 has a length that extends from the surface of the upper electrode 15 to the surface of the lower electrode 13 and is about 1.3 μm. A wiring connecting area 17 is made open at an exposed spot of the surface of the insulating film 14 and the surface of the lower electrode 13 is hence exposed. A voltage measuring device 20 for potential difference measurement is connected between the upper electrode 15 and the lower electrode 13 via wirings 18 and 19.
As mentioned above, the contact hole diameter in the leading-edge 65 nm generation or later is φ0.1 μm and the aspect ratio is as large as 10. Upon the formation of such contact holes 16, it is difficult to obtain a vertical shape even though the plasma etching technology is used. The contact hole becomes easy to tend to assume a forward taper (the diameter of the lower portion of the contact hole 16 is smaller than that of the upper portion thereof). It is also difficult to bring the contact hole to an inversely-tapered shape by plasma etching. In a plasma etching process step, positive ions h and electrons e are launched into a film to be etched thereby to cause etching. The positive ions h and the electrons e are identical in the amount of incidence. Since, however, the electrons e are larger than the positive ions h in transverse momentum, the electrons e do not enter vertically so much as compared with the positive ions h where the ratio of the depth D2 of each contact hole 16 to the diameter D1 thereof is large. Therefore, some electrons e which collide with an inner wall surface of the contact hole 16 and cannot reach the contact hole bottom, exist in the electrons e migrated to the bottom of each contact hole.
On the other hand, the positive ions h reach the bottom of each contact hole 16 without colliding with the inner wall surface of the contact hole 16 so much as compared with the electrons e. Therefore, the positive ions h rather than the electrons e are much stored at the contact hole bottom. Since the electrons e are much deposited at the upper portion of the contact hole 16, charge polarization, i.e., charge-ups occur at the upper and lower portions of the contact hole 16. The occurrence of the charge-ups leads to the problems such as the reduction in etching rate, the stop of etching as described above.
A method of quantitatively measuring a charge-up using the plasma process detecting sensor 10 shown in FIG. 5 will next be explained.
When the sensor 10 is exposed to the plasma 21 corresponding to an environment for a plasma etching condition, the upper electrode 15 become negatively charged and the contact hole bottom, i.e., the lower electrode 13 becomes positively charged, whereby a charge-up occurs. The degree of this charge polarization (charge-up amount) is measured by the voltage measuring device 20 as a difference in potential between the upper electrode 15 and the lower electrode 13, and hence the charge-up amount for the plasma etching condition can be measured quantitatively.
Although, however, the previous proposal of the inventors, et al. of the present application can solve the problems or imperfections of the related arts, there is a possibility that such a problem as shown in FIG. 6 will occur.
FIG. 6 is a view for describing damage to the inner wall surface of the contact hole 16 due to the positive ions h shown in FIG. 5.
When the sensor 10 is exposed to a plasma etching environment, a small part of the positive ions h collides with the inner wall surface of the contact hole of the insulating film 14 that assumes the forward tapered shape. Therefore, the inner wall surface of the contact hole formed in the insulating film 14 undergoes physical damage due to the collision. The physical damage is specifically a defect in the insulating film 14 and has a defect level that assists electric conduction to the electrons e. Namely, as the defect level due to the collision of the positive ions h increases, the resistance of the inner wall surface of the contact hole formed in the insulating film 14 is reduced, so that the current (electrons) become easy to flow. In doing so, the electrons e stored with being polarized to the upper electrode 15 migrate from the upper electrode 15 to the lower electrode 13 via the defect level thereby to cancel out the positive ions h deposited with being polarized to the lower electrode 13. Therefore, the degree of charge polarization becomes small (charge-up amount is reduced) and the difference in potential between the upper electrode 15 and the lower electrode 13 is reduced. Namely, as the time to expose the sensor 10 to the plasma etching condition becomes longer, there is a possibility that it will not be possible to measure the difference in potential, and there is a possibility of occurrence of a problem that age deterioration of a sensor function will take place during the measurement of a charge-up.